Production of a cellular macromolecular synthesis inhibition factor(s) in gypsy moth cells infected with the Autographa californica nuclear polyhedrosis virus

The gypsy moth cell lines IPLB-Ld652Y and IPLB-LdFB have been shown to be semipermissive for replication of the Autographa californica multiple-embedded nuclear polyhedrosis virus (AcMNPV). We report here that AcMNPV infection of these cell lines results in the production, by the infected cells, of a proteinaceous viral derived factor(s) which is secreted into the tissue culture medium (IPL-52B). Uninfected IPLB-Ld652Y and IPLB-LdFB cells, when incubated with media from AcMNPV-infected cells, exhibit markedly reduced levels of cell growth, mitosis, DNA, and protein synthesis. The factor(s), which has been designated the macromolecular synthesis inhibition factor (MSIF), is produced and secreted from infected cells between 1 and 30 hr postinfection and is produced in the absence of viral gene activity in infected cells. A preliminary characterization of the MSIF revealed the presence of a heat-labile, proteinaceous, pH sensitive molecule(s) whose activity was neutralized by three different monoclonal antibodies directed against the AcMNPV 64-kDa envelope glycoprotein. Production of the MSIF(s) did not require any new viral or cellular gene activity and was inhibited by treatment of infected cells with the lysosomal protease inhibitor, leupeptin. It is postulated that the MSIF is the AcMNPV 64-kDa glycoprotein or some component or complex of this protein, which is removed from the inoculum virus, and secreted, by the infected cells, into the tissue culture medium.